Mean Length Of Fish Research Articles

EFFECT OF DIETARY ASTAXANTHIN ON GROWTH, SURVIVAL RATE AND PIGMENTATION OF COMMERCIAL CLOWNFISH, Amphiprion ocellaris

This study examined the influence of astaxanthin added to food on growth, survival rate and pigmentation of commercial false clownfish, Amphiprion ocellaris. Five experiments were performed with synthetic astaxanthin contents: 0; 50; 100; 150 and 200 mg/kg diets. Mean weight and mean length of fish were 1.16 ± 0.22 gand and 33.05 ± 3.29 mm respectively. Fish were fed by 5% of their live weight during the examination of 8 weeks. After 56 days of experiments, the skin pigmentation levels were analysed using Clownfish Exercise pigmentation chart which has a scale from 1 to 10. Color scales of 5 experiments: 0; 50; 100; 150 and 200 mg Astaxanthin/kg diets were 2.12 ± 0.08, 3.79 ± 0.1, 5.31 ± 0.14, 7.78 ± 0.09, 8.04 ± 0.12 respectively. The result showed that the dietary astaxanthin could increase coloration of skin compared with the control group which had the lightest color (P < 0.05) but there were no significant effects on growth and survival rate of clownfish (P > 0.05).

Measuring fish length and assessing behaviour in a high-biodiversity reach of the Upper Yangtze River using an acoustic camera and echo sounder

Summary In the past decade improved acoustic hard- and software have enabled estimations of abundance and distribution patterns of aquatic organism, including non-intrusive monitoring of fish migrations and behaviour. In this study, a high frequency acoustic camera (DIDSON-LR, 1.2 MHz, 0.7 MHz) and a portable split-beam scientific echo sounder (Simrad EY60, 200 kHz) collected acoustic data on 192 and 157 individuals within 24 hr (19–20 April 2011) in the Mituo reach of the Yangtze River, China. Mean fish length estimated from the acoustic camera data was 18.7 ± 5.6 cm, with an average swimming speed of 0.19 ± 0.13 m s−1. The mean fish target strength (TS) produced by the echo sounder was −43.8 ± 4.4 dB, which corresponded to 5.7–119.9 cm fish length when converted by three different TS-length equations. Average swimming speed was 0.11 ± 0.06 m s−1 from the echo sounder. Compared with the actual fish catch by the three layers of drift gill net in the survey area, the target length indicated by DIDSON was more accurate than the EY60 results, which were highly affected by the choice of TS length equations. It was determined that the two devices used synchronously could estimate fish length effectively to investigate their behaviour and distribution.

Fish on the roof of the world: densities, habitats and trophic position of stone loaches (Triplophysa) in Tibetan streams

The fast increase in temperature on the Tibetan Plateau, with anticipated future changes in aquatic ecosystems and biodiversity, highlights the urgent need for ecological data on the sparsely studied Tibetan running waters. In the present study we surveyed eight Tibetan streams to obtain data on densities, feeding selectivity and trophic position of the stone loach Triplophysa. Benthic algae, detritus, macroinvertebrates and fish were quantified and collected for stable isotope and stomach content analysis. Triplophysa density (mean 0.70 individuals m–2, maximum 1.6 individuals m–2) decreased with altitude and increased with the percentage cover of fine substratum. Glacier-fed sites tended to have the lowest fish densities, whereas the highest densities were found near lakes. Mean fish length (4.1–9.6cm) was positively related to the percentage cover of coarse substratum. Triplophysa was omnivorous, but the composition of the stomach contents varied greatly between sites and among individuals. Algal matter was ingested at most sites, but macroinvertebrates (Chironomidae, Baetidae and Simuliidae) dominated the ingestion (average 50–100%). The trophic position of Triplophysa, identified from δ15N (‰) of the biota, varied between 2.6 and 4.2 among localities (mean 3.6) and was inversely related to the biomass of benthic algae, but unrelated to quantities of other potential food sources.

Fine-scale spatial association between baleen whales and forage fish in the Celtic Sea

Baleen whales can be regularly observed in the Celtic Sea; however, little is known about their local foraging behaviour. The study objective was to determine whether or not baleen whales selectively prey upon particular forage fish species or, on the contrary, is predation on the Celtic Sea plateau driven by random encounters between prey and predator? Concurrent sighting surveys for fin (Balaenoptera physalus), minke (Balaenoptera acutorostrata), and humpback (Megaptera novaeangliae) whales were carried out simultaneously from 2007 to 2013 during dedicated fisheries acoustic surveys assessing the abundance and distribution of forage fish. Probabilities of spatial overlap between baleen whales and forage fish were analysed and compared with the probability of a random encounter. For estimations of foraging threshold and prey selectivity, mean fish biomass and fish length were calculated when baleen whales and forage fish co-occurred. Whales were dominantly observed in areas with herring (Clupea harengus) and sprat (Sprattus sprattus), while areas with mackerel (Scomber scombrus) were not targeted. A prey detection range of up to 8 km was found, which enables baleen whales to track their prey to minimize search effort. Fish densities within the defined foraging distance ranged from 0.001 to 3 kg·m−2 and were correlated to total fish abundance. No prey size selectivity according to fish length was found. By linking baleen whale distribution to high-density herring and sprat areas, it was possible to identify the Celtic Sea as a prey hot spot for baleen whales during autumn.

Ecological indicators to capture the effects of fishing on biodiversity and conservation status of marine ecosystems

IndiSeas (“Indicators for the Seas”) is a collaborative international working group that was established in 2005 to evaluate the status of exploited marine ecosystems using a suite of indicators in a comparative framework. An initial shortlist of seven ecological indicators was selected to quantify the effects of fishing on the broader ecosystem using several criteria (i.e., ecological meaning, sensitivity to fishing, data availability, management objectives and public awareness). The suite comprised: (i) the inverse coefficient of variation of total biomass of surveyed species, (ii) mean fish length in the surveyed community, (iii) mean maximum life span of surveyed fish species, (iv) proportion of predatory fish in the surveyed community, (v) proportion of under and moderately exploited stocks, (vi) total biomass of surveyed species, and (vii) mean trophic level of the landed catch. In line with the Nagoya Strategic Plan of the Convention on Biological Diversity (2011–2020), we extended this suite to emphasize the broader biodiversity and conservation risks in exploited marine ecosystems. We selected a subset of indicators from a list of empirically based candidate biodiversity indicators initially established based on ecological significance to complement the original IndiSeas indicators. The additional selected indicators were: (viii) mean intrinsic vulnerability index of the fish landed catch, (ix) proportion of non-declining exploited species in the surveyed community, (x) catch-based marine trophic index, and (xi) mean trophic level of the surveyed community. Despite the lack of data in some ecosystems, we also selected (xii) mean trophic level of the modelled community, and (xiii) proportion of discards in the fishery as extra indicators. These additional indicators were examined, along with the initial set of IndiSeas ecological indicators, to evaluate whether adding new biodiversity indicators provided useful additional information to refine our understanding of the status evaluation of 29 exploited marine ecosystems. We used state and trend analyses, and we performed correlation, redundancy and multivariate tests. Existing developments in ecosystem-based fisheries management have largely focused on exploited species. Our study, using mostly fisheries independent survey-based indicators, highlights that biodiversity and conservation-based indicators are complementary to ecological indicators of fishing pressure. Thus, they should be used to provide additional information to evaluate the overall impact of fishing on exploited marine ecosystems.

The Influence of Bait and Stereo Video on the Performance of a Video Lander as a Survey Tool for Marine Demersal Reef Fishes in Oregon Waters

AbstractWe evaluated how the use of bait as a fish attractant influenced the species and size composition of demersal fishes viewed with a stereo video lander at 160 sampling sites at Stonewall Bank, a deepwater rocky reef complex off the Oregon coast. We also studied the effectiveness of stereo video for generating estimates of fish length and distance from the cameras. Bait altered the species composition of fish encountered, increasing the mean counts of demersal fishes by 47%, with increases of 135–250% for Rosethorn Rockfish Sebastes helvomaculatus, Northern Ronquil Ronquilis jordani, and Spotted Ratfish Hydrolagus colliei. Increases in the mean counts of 35–150% for unidentified sculpins (Cottidae), Yelloweye Rockfish S. ruberrimus, and Quillback Rockfish S. maliger were nonsignificant. The calibrated stereo video lander provided acceptably precise estimates of fish length and camera‐to‐fish distance (range of three replicate measurements less than 3 cm for length and 20 cm for distance) for 34.3% of the demersal fishes that were counted. The precision of length and distance estimates declined with increased distance; acceptable estimates of distance were typical when fish were within 200 cm and were infrequent when fish were beyond 500 cm. Bait reduced the mean distance at which acceptable estimates of length and distance were obtained from 264 cm to 200 cm, but had no effect on mean fish length for the three most frequently encountered demersal species. The combined effect of bait on demersal fish counts and mean distance more than doubled the efficiency of the stereo video lander for generating fish length and fish–camera distance estimates.Received January 22, 2014; accepted April 9, 2014

Marine protected areas for deepwater fish populations: an evaluation of their effects in Hawai’i

The success of marine protected areas (MPAs) as a tool for conservation and fisheries management has been well documented. However, these results have typically been seen in shallow water systems and questions remain whether this management strategy could be successfully applied to deepwater ecosystems. Our objectives were to determine the efficacy of four deepwater MPAs called bottomfish restricted fishing areas (BRFAs), with various time spans of protection, monitored at depths between 90 and 310 m from 2007 to 2011 for six species of deepwater snapper and one grouper harvested in the Main Hawaiian Islands. Our results suggested that the duration of protection influenced reserve effects, particularly for target species. Mean fish length, and in some cases abundance, increased for one or more of the most economically important target species inside nearly all tested BRFAs. In addition, more mature fish were seen inside the BRFA with the longest duration of protection (~14 years); species richness increased outside this area while inside it remained the same. Here, we provide the first evidence that deepwater MPAs can have positive effects on deepwater species and that many protection effects were consistent with results found in shallow water ecosystems. While these findings are novel, additional data over greater temporal scales will be necessary to determine whether these trends will continue and if others will become important over time.

Assessment of sábalo (Prochilodus lineatus) fisheries in the lower Paraná River basin (Argentina) based on hydrological, biological, and fishery indicators

This study assesses the change in fish exploitation patterns of the sábalo fisheries of the lower Paraná River basin based on hydrological, biological, and fishery indicators. From historical catch records, we recorded a shift from a lightly and moderate exploited status before 2001 to a heavily exploited one, as a result of the development of sábalo exports from 2001 onwards. Channel and floodplain connectivity indices demonstrated that the Paraná exhibited highly favorable hydrological conditions between 1972 and 1999 but more adverse conditions from 1999 to 2009, as a consequence of flood pulses reduction coincident with a fishing mortality increment. A total catch of 15,000 tons, including local consumption, regional market, informal sales, and exportation volumes, was estimated as the maximum sustainable catch. That level was instead exceeded 3 fold in 2004, in parallel with a decrease in the mean fish length from 48 to 42 cm, along with a reduction in both the mesh size from 16 to 12 cm and megaspawner proportion, and an increase of fishing mortality. Although growth overfishing was not noted, an analysis of the spawning potential ratio trend indicated that recruitment overfishing took place during 2005, since the fishing mortality rate was 4 times greater than the natural mortality rate. These observations suggest that less favorable hydrological conditions after 1999 coupled with a coincident high fishing pressure could have impacted the sábalo population biomass. Management of sábalo fisheries requires to set aside a single economic vision of the resource use moving to an ecosystem-oriented approach that incorporate, among others components, the hydrological regime, species life history traits, fishing impacts on other species, and main stakeholders socioeconomic requirements as key elements for the preservation of fishery sustainability.

Parasites and hepatic histopathological lesions in lisa (Mugil incilis) from Totumo mash, North of Colombia

ABSTRACTObjective. To assess the levels of parasitism by nematodes and trematodes, as well as the hepatic histopathological alterations present in Mugil incilis (Lisa) from Totumo marsh, North of Colombia. Materials and methods. Between July 2004 and June 2005, 500 fish were collected at Totumo Marsh (75°16’W and 10°44´N), North of Colombia. Morphometric and parasitic parameters were determined for each specimen, and the hepatic histopathological status of the liver was assessed by analyzing liver slides stained with hematoxylin and eosin. Results. Nematode larvae isolated from Mugil incilis corresponded to Contracaecum spp. Parasite prevalence was 60.49%. Parasitic mean abundance and mean intensity were 4.8±1.05 and 7.02±1.49, nematodes per fish, respectively. The correlation between nematode mean abundance and fish length was significant and positive (r=0.525, p<0.0001), but negative for condition factor (r=-0.109, p=0.014). Hepatic histopathological analysis revealed the presence of encapsulated trematode larvae as the main finding. However, the presence of inflammation, granulomas, steatosis and necrosis, were also registered as secondary alterations. Conclusions. Lisas collected at Totumo Marsh are parasitized with nematodes and trematodes. These fish have different histopathological lesions in the liver tissue, being the most important the presence of trematode encapsulated cyst that generate inflammatory reactions, and negatively correlate with morphometric markers of fish health.

Circle Hook Requirements in the Gulf of Mexico: Application in Recreational Fisheries and Effectiveness for Conservation of Reef Fishes

In 2008, recreational anglers in the us Gulf of mexico were required to use circle hooks when catching federally managed reef fishes (50 C.F.R. 622.41). From June 2009 through november 2010, we observed recreational hook-and-line fishing during for-hire trips off the west coast of florida. Anglers used circle hooks and other hook types in a wide range of sizes from a variety of manufacturers. The present study evaluated the effectiveness of circle hooks toward reducing potentially lethal hooking injuries and the number of undersized reef fishes caught in the florida recreational fishery. For seven out of 10 species evaluated, there were significant reductions in potentially lethal injuries for fish caught with circle hooks compared to all other hook types. Overall, reductions ranged from 30% to 93%. Potentially lethal injuries for red snapper [Lutjanus campechanus (poey, 1860)] were reduced to 6.3% with circle hooks (from 17.1% with other hook types), which was a 63.5% reduction. For gag [Mycteroperca microlepis (Goode and Bean, 1879)] and scamp (Mycteroperca phenax Jordan and swain, 1884) potentially lethal injuries were <5.5% for both circle hooks and other hook types and differences were not significant. There was no clear evidence that circle hooks reduced bycatch of undersized fishes when compared to J-hooks. There was an increase in mean fish length with increasing circle hook size for multiple species; however, r2 values were low and much of the explained variance was unrelated to circle hook size.

Selenium:mercury molar ratios in fish from the Savannah River: implications for risk management

The risk to humans from contaminants in fish is dealt with by issuing consumption advisories, which are devised from consumption patterns, contaminant levels, and toxicity of those contaminants. The primary contaminant of concern in fish is mercury, and recently it has been suggested that the protective effects of selenium on mercury toxicity should be considered in risk management. The relationships between mercury, fish species and fish size, and selenium:mercury (Se:Hg) molar ratios were examined for freshwater fish from the Savannah River. The data indicated: (1) significant variation in Se:Hg molar ratios among and within species, (2) mean selenium molar ratios for the 11 species were negatively correlated with mean mercury levels and mean fish length, (3) greater variation in individual variances within species than the variation in mean ratios among species, (4) some species with high mean ratios had individuals with ratios below 1, and (5) even the species with the highest mean ratios had some individuals close to a molar ratio of one. These data suggest that the great variability of the Se:Hg molar ratios within a species results in the ratios being unpredictable. That is, knowing the mean Se:Hg molar ratio for a given species does not predict the ratios of individuals, or thus the protectiveness of selenium on mercury toxicity.

Thermal habitat for 0-group fish in the Barents Sea; how climate variability impacts their density, length, and geographic distribution

AbstractEriksen, E., Ingvaldsen, R., Stiansen, J. E., and Johansen, G. O. 2012. Thermal habitat for 0-group fish in the Barents Sea; how climate variability impacts their density, length, and geographic distribution. – ICES Journal of Marine Science, 69: 870–879. Between 1980 and 2008, the climate changed from cold to warm conditions in the Barents Sea. Warmer conditions have been indicated as favourable for cod, haddock, and herring recruitment and unfavourable for capelin, although during recent years these relationships have weakened and need to be revised. Extensive survey observations of temperature and 0-group cod, haddock, herring, and capelin are explored, a bounded temperature range occupied by ∼80–90% of 0-group fish (core thermal habitat, CTH) defined for each species, and an analysis made of how climate variability influenced density, length, and geographic distribution. Maximum fish densities were at 6.2°C for cod, 7.2°C for haddock, 7.0°C for herring, and 5.1°C for capelin. The area of CTH for cod, haddock, and herring increased from cold to warm years, as did the occupation area of each species. Capelin underwent a northeast distributional shift from cold to warm years. The 0-group fish were observed in a broad range of temperatures of −1 to 10.5°C. However, fish densities showed a dome-shaped distribution with temperature. Mean fish length was 7.1 cm for cod, 8.9 cm for haddock, 7.0 cm for herring, and 4.6 cm for capelin, with length distributions exhibiting a non-uniform response to temperature.

Shifts in Prey Selection and Growth of Juvenile Pikeperch (&amp;lt;i&amp;gt;Sander lucioperca&amp;lt;/i&amp;gt;) over Half a Century in a Changing Lake V&amp;#245;rtsj&amp;#228;rv

Analysis of historical and recent data is essential to understand how eutrophication and/or climate change might trigger shifts in the feeding mode of fish and trophic dynamics of shallow lakes. To assess long-term changes in the diet and growth of juvenile pikeperch (Sander lucioperca), the prey selection and growth of pikeperch fry from Lake Vortsjarv was investigated in 2007 - 2010 and compared with data from 1920 to 1970. Over the observed period, larger cladocerans have become less frequent in the diet as eutrophication has altered the zooplankton community. Furthermore, climate change has triggered a mismatch between the predator and its prey: the smelt population has collapsed but other fish fries are too large for YOY (young-of-the-year) pikeperch. However, the mean length of fish has decreased mainly due to the postponed diet shift.

Impacts of fishing by dewatering on fish assemblages of tropical floodplain wetlands: A matter of frequency and context

Tropical floodplain wetlands and the fish communities they support are subject to great pressure from human demands for water and aquatic living resources. In densely populated agricultural areas where such pressures are greatest, floodplain wetlands may be dewatered for the dual purpose of crop irrigation and fish harvesting. Viewed as highly destructive to fish communities, the practice is widely discouraged but remains common. We investigated the impacts of dewatering on fish abundance and assemblage structure in permanent floodplain wetlands of the lower Mekong region. Draining was carried out only in wetlands where access for fishing and water withdrawal was exclusive to individual households or groups, and where fishing was restricted to draining events. Subsequently, the impacts of draining were found to be equivalent to those of intensive fishing, rather than entirely catastrophic. Many wetlands were drained and fished repeatedly in a single dry season, with catches declining by 72% on average between consecutive events. Species richness and mean length of fish also declined with consecutive dewatering events. Fish biomass was higher in drained wetlands prior to the first and second draining events than in open access, non-drained wetlands. These surprising results suggest that draining of floodplain wetlands is not as fundamentally destructive to fish populations as is often assumed. Where fishing pressure under open access conditions is high, allocation of exclusive rights to fish and dewater wetlands can aid fish conservation as long as dewatering is carried out only once.

Global variation in marine fish body size and its role in biodiversity–ecosystem functioning

To date, investigations of the positive re- lationships between biodiversity and ecosystem func- tioning among global marine ecosystems, and the management initiatives derived from these studies, have focused exclusively on species richness. We hypothesize that body size variations that occur among size-structured aquatic ecosystems subjected to ex- ploitation may also contribute to these patterns. Our analyses of maximum lengths of 12 151 fish species from 56 exploited large marine ecosystems (LMEs) revealed a 2-fold variation in geometric mean lengths, that were strongly and negatively correlated with spe- cies richness. LMEs characterized by larger mean sizes were also skewed towards dominance by large spe- cies. The expected positive and significant correlation between mean fish length and latitude (characterized as Bergmann's Rule) was observed among North Atlantic, South Pacific, and Indian Ocean (southern lat- itudes) LMEs, but not in 3 other regions, including the North Pacific. In the North Atlantic, anomalous long- term declines in top predator catch rates (one measure of ecosystem functioning) occurred, and within tem- perate North Atlantic LMEs, species size distributions were more skewed towards large species relative to North Pacific LMEs. Our global analyses indicate that fish body size may act as a factor of considerable importance in mediating the relationship between global marine fish species richness and ecosystem functioning, and that management initiatives to ensure ecosystem stability in the face of exploitation should include the restoration and maintenance of this impor- tant functional trait.

Trend analysis of indicators: a comparison of recent changes in the status of marine ecosystems around the world

Abstract Blanchard, J. L., Coll, M., Trenkel, V. M., Vergnon, R., Yemane, D., Jouffre, D., Link, J. S., and Shin, Y-J. 2010. Trend analysis of indicators: a comparison of recent changes in the status of marine ecosystems around the world. – ICES Journal of Marine Science, 67: 732–744. Time-series of ecological and exploitation indicators collected from 19 ecosystems were analysed to investigate whether there have been temporal trends in the status of fish communities. Using linear and non-linear statistical methods, trends are reported for six indicators (mean length of fish in the community, mean lifespan, proportion of predatory fish, total biomass of surveyed species, mean trophic level of landings, and inverse fishing pressure), and the redundancy of these indicators across ecosystems is evaluated. The expected direction of change for an ecosystem that is increasingly impacted by fishing is a decline in all indicators. A mixture of negative and positive directions of change is recorded, both within and among all ecosystems considered. No consistent patterns in the redundancy of the ecological indicators across ecosystems emerged from the analyses, confirming that each indicator provided complementary information on ecosystem status. The different trends in indicators may reflect differing historical exploitation patterns, management, and environmental regimes in these systems. Commitment to monitoring programmes and development of system-specific baseline, target, and threshold reference levels are required. Improved understanding of the responsiveness and performance of ecological indicators to management actions are needed to address adequately whether ecosystems are recovering from, or being further impacted by, fishing, and whether management targets are being met. The relative effects of multiple environmental and ecological processes as well as multiple human-induced stressors that characterize exploited ecosystems also need to be quantified.

Possibilities of using the length differentiation of hatchery sea trout, Salmo trutta m. trutta L., parr to predict numbers of one-year smolts

Growth and smoltification were followed during the first year of life in 14 full sibling families of sea trout, Salmo trutta m. trutta L., originating from the Vistula stock. Until January, the families were reared separately, and then together after they had been PIT tagged. The degree of smoltification was evaluated in the second spring. Smolts were noted in each family. The percentage of these, which ranged from 14 to 66%, depended on mean fish length in October (r 2 = 0.338) and January (r 2 = 0.346). In either October or January the fish that smolted next spring were, on average, longer than those that did not, but this difference was not manifested by the bimodality of length distribution, and it did not allow predicting the number of smolts based on division of distributions of fish length in autumn or winter into Gaussian components.

Factors affecting between‐lake variation in the occurrence of epidermal papillomatosis in roach,Rutilus rutilus(L.)

The theory of island biogeography predicts that the probability of a species occupying an island depends on a dynamic equilibrium between extinction and colonization. Epidermal papillomatosis is a disease manifesting as skin tumours on fish. We studied the factors affecting the occurrence of the disease in roach, Rutilus rutilus (L.), in 34 lakes. The results of discrimination analysis suggest that maximum depth, percentage of the drainage area of the lake covered by lakes in the vicinity and altitude best identified diseased lakes. Comparison of diseased and non-diseased lakes revealed that lake area could also be regarded as a variable contributing to the occurrence of the disease. The sampling date, proportion of males and mean length of fish did not discriminate between the lakes. The probability of the disease occurring was highest in large, deep, low-altitude lakes which had a high percentage of lakes in their vicinity. Thus, the results indicate that the colonization and extinction processes probably contribute to the occurrence of papillomatosis in roach, as predicted by the theory. Furthermore, the large natural variation in the occurrence of the disease could mask possible environmental effects and between-lake comparisons should be interpreted with caution when using the fish-papillomatosis system as an indicator of environmental stress.

Abstracts: 39th Annual Meeting of the American College of Veterinary Ophthalmologists, Boston, MA, USA, October 15–18, 2008

Purpose: The aim of this study was to evaluate the ocular features and intraocular pressure (IOP) in adult Red Drum Fish (Sciaenops ocellatus). Methods: All fish were anesthetized with tricaine methanesulfonate (MS-222, Western Chemicals, Ferndale, WA, USA) at 70 parts per million. The anterior segment of all fish eyes were examined with a Finnoff transilluminator and slit-lamp biomicroscopy. Binocular indirect ophthalmoscopy was performed in all eyes to observe the posterior segment. IOP was measured and recorded in both eyes of 13/18 fish and in the right eye only in 1/18 fish using applanation tonometry (27/36 total eyes). Tonometry readings were discarded in 4 fish (8 eyes) due to poor anesthesia and inadequate restraint. The horizontal corneal diameter was measured in all eyes. Results: There were 9 male and 9 female fish, all of which were 5 years old. Ophthalmic examination of the anterior segment revealed a horizontal oval-shaped immobile pupil. A characteristically large spherical lens and shallow anterior chamber often exhibiting an aphakic crescent medially was observed. The retina was anangiotic and the fundus ranged in color from white-gray to dark yellow-gray. The optic nerve papilla was horizontally elongated and associated with a prominent hyaloid vessel projecting anteriorly into the vitreous. In 2/36 eyes, 2 mm white translucent cysts in the anterior chamber were identified. Seventeen of the fish had anterior subcapsular opacities in both eyes. These lens opacities were between 1 and 5 mm in diameter and ranged in density from faint to prominent. The subcapsular opacities were central to paraxial. One eye had multifocal lens opacities. The mean horizontal corneal diameter of both eyes was 20.83 ± 1.42 mm. The mean IOP for the right and left eye of fish was 8.69 ± 3.29 mmHg and 6.82 ± 3.19 mmHg, respectively. Mean fish length was 99.05 ± 4.33 cm. Conclusions: The ocular features of a group of adult Red Drum Fish were identified. In this population of red drum, anterior subcapsular cataracts were a common finding. The average IOP this population of fish was determined to be 7.82 ± 2.82 mmHg.

Length Variation in Age‐0 Westslope Cutthroat Trout at Multiple Spatial Scales

AbstractPhenotypic diversity provides ecological and evolutionary functions, stabilizing populations in variable environments. Although benefits of larger body size in juvenile fishes are well documented, size variation may have value as well. We explored the distribution of length and length variation in age‐0 westslope cutthroat trout Oncorhynchus clarkii lewisi at three spatial scales: area (102 km2), stream (101 km2), and site (100 km2). In addition, we examined relationships between length variables (mean length and interquartile range of length) and instream (temperature and conductivity) and landscape (aspect, elevation, headwater distance, and valley width) variables that were expected to be associated with fish size. Conductivity was included as a surrogate for productivity. Most variation in mean length and interquartile range of fish length was found among areas (62.2% and 62.6%, respectively). Mean length also varied among streams and sites (21.9% and 15.8%, respectively). Similarly, interquartile range of fish length varied among streams and sites (19.1% and 18.3%, respectively). Both length variables were associated with temperature and elevation. Mean fish length was also associated with conductivity, but the association between interquartile length range and conductivity was weak. We conclude that the conservation of variation in phenotypic attributes, such as length, in westslope cutthroat trout may require conservation of viable populations across broad areas and across environmental gradients that are associated with growth.